Turbochargers are forced-induction devices that are utilized to increase the pressure of the intake air provided to the engine. A turbocharger may be driven by exhaust from the engine. More particularly, exhaust gas from the engine is routed to the turbocharger and to rotate a turbine wheel, which in turn rotates a compressor wheel. The compressor wheel, thereby, pressurizes and supplies intake air to the engine, which may increase the power output of the engine as compared to an otherwise comparable naturally-aspirated engine. The pressure of the air supplied to the engine may be referred to as a boost pressure.
An amount of exhaust gas routed to the turbocharger may vary based on the speed of the engine (e.g., revolutions per minute or RPM). For example, a lower RPM value will result in less exhaust gas than a higher RPM value. Exhaust gas flowing through a fixed inlet area will, thus, have a lower flow velocity with lower engine speed and a higher flow velocity with higher engine speed. As a result, the lower flow velocity of the exhaust will result in a lower turbine speed and the higher flow velocity will result in a higher turbine speed. The lower and higher turbine speeds, respectively, result in lower and higher boost pressure from the compressor wheel.
To control boost pressure over a range of engine speeds, turbochargers may include variable turbine geometry (VTG) assembly, which varies an effective inlet area to the turbine wheel. The VTG assembly includes a plurality of vanes circumferentially distributed around the turbine wheel. The vanes are selectively rotated in order to change an effective geometry of the turbine housing and, in particular, change the effective inlet area. For example, at low engine speed, the vanes may be rotated to a more closed position, which reduces the inlet area, so as to increase velocity of the exhaust gas flowing to the turbine wheel. Conversely, at high engine speed, the vanes may be rotated to a more open position, which increases the inlet area, so as to accommodate a greater flow rate of the exhaust gas flowing the turbine wheel. Accordingly, the speed of the turbine wheel and, thereby, the boost of the turbocharger may be controlled over a range of engine speeds.
Each vane may be rotated by a respective vane lever. The vane levers may be rotated in unison, for example, by an adjustment ring that is adapted to be selectively rotatable between a first position and a second position. As the adjustment ring is rotated, portions of the adjustment ring engage each vane lever, which causes the vane levers to move, thereby causing the vanes to rotate. Furthermore, vibratory and other forces applied to the turbocharger may cause the adjustment ring and/or the levers to rattle into each other, which may cause vibrations and/or noise perceptible by the user and/or may cause wear of the adjustment ring and/or vane levers.